The present invention relates to an improved polymor articular prosthesis and to its preparation process. More specifically, it relates to a total or partial articular prosthesis, whose properties have been improved both with respect to the friction coefficients of its sliding surface and with respect to its resistance to deformation.
For some years now, the problems caused by the treatment of patients such as those suffering from arthrosis of the hip have been solved by surgical operations consisting of removing the attached parts of the joint and replacing them by metallic, ceramic or plastic prostheses in order to obtain friction coefficients compatible with a satisfactory operation of the joint.
The human joint has in fact a particularly low friction coefficient and the specific properties of the synovia and the cartilage enable the joint to respond to the needs resulting from long-term frictional work under stress.
When it is necessary to use articular prostheses, it is not the intention to replace all the mechanisms controlling a healthy joint, but solely to fit new articular surfaces, whilst then assisting the adaptation to the prosthesis of the neuromuscular control, the ligament system, the capsule and the synovia, every effort being made to preserve their functions.
In order to facilitate this adaptation, the prostheses are made so as to be able to reproduce as faithfully as possible the natural shapes and the geometry of the joint. Moreover, the choice of the materials used for the prosthesis is very important, in view of the sliding properties which it must have and the forces exerted on the hinge points constituted by the joints. Thus, the articular sliding surfaces must have an easy friction, but must not wear to an exaggerated extent, because it is necessary to prevent the formation of wear debris or fragments which, as a function of their grain size, could lead to inflammation.
Hitherto, articular prostheses have been made from metal, ceramics or plastics.
Metallic prostheses have the disadvantage of leading to the formation of wear debris, which is very unsatisfactorily tolerated when the sliding surfaces of the joint are both made from metal. Metallic prostheses have in any case been largely abandoned, due to their defects.
Ceramic prostheses have the advantage of very low friction coefficients when used either in direct contact with the healthy part of a joint, or in contact with a polyethylene or ceramic part. However, they have the disadvantage of being fragile and brittle, which leads to in vitro breaking accidents.
Plastic prostheses are generally used in contact with a metallic part, which makes it possible to obtain a very low friction coefficient of the joint. The metal is either a chromium - cobalt alloy, or stainless steel and the plastic prosthesis is generally made from high density polyethylene. However, these articular prostheses have the disadvantage of leading to the formation of relatively well tolerated, but unacceptable wear debris, whilst suffering from deformations due to creep, which are prejudicial to the satisfactory functioning of the prosthesis.